Update CI config

.gitlab-ci.yml

-image: python:2.7
+image: python:3.7
 build:
   script:
     - pip install coveralls

requirements_test.txt

-django==1.8.8
-
-djangorestframework==3.3.2
-djangorestframework-jwt==1.7.2
-
-django-cors-headers==1.1.0
-django-extensions==1.5.5
-django-filter==0.10.0
-django-permission==0.8.8
-djangorestframework-composed-permissions==0.1
-
-markdown==2.6.2
-werkzeug==0.10.4
-django-debug-toolbar==1.3.2
-mock==1.3.0
-django-rest-swagger==0.3.4
+django==2.0.13
+djangorestframework==3.7.*
+djangorestframework-jwt==1.8.0
+django-cors-headers==2.3.0
+django-filter==2.0.*
+django-permission==1.0.4
+djangorestframework-composed-permissions==0.2.1
+psycopg2==2.8.4
+openssl
+markdown
+werkzeug
+mock